If you are like me then the very first thing you do when you get a brand new device like the Nexus 9 is find out how to root it. Then you go looking for a custom recovery and some roms. If you are going to do that then you will want to make sure you have a way of flashing your device back to factory in case you mess something up and soft brick your device, or just in case you want to get your device back to stock so you can accept the latest OTA. Google began rolling out the Android 5.0 Lollipop Stock Image for the Volantis Nexus 9 tablet yesterday. You won't even need to download the binaries separately as was the case on older Nexus devices since they are built in to the stock image. Stock images for other Nexus devices should be updated soon.
Via Google Developers